Does it look like hair from your head or is it coarser like hair from "down there". (and yes I know coarser isn't a word) If it is thicker and "more coarse" then you might have a macro algea like maidens hair. Still spreads but not like a carpet of filed of grass.
Hair algea spreads over EVERYTHING. It also doesn't look that attractive as it spreads. Unfortunalty it is rather hard to get rid of.
Maidens hair is better looking but has a problem with clogging things up. Mine grew in clumps... looked great... very dark green, very healthy. Unfortunatley it also broke loose in clumps and cloged PH, skimmers, overflows, you name it, it found a way.
Maidens hair, IMHO, belongs more in the 'fuge than in the display... unless you have a sally lightfoot, emerald crab, or (in my case) a flame angel. They will eat everything they can reach.
Good Luck.
PS what is you phosphate and silica reading? How old are your lights?